Yep that totally makes sense, can't expect to transfer more data concurrently than the fattest pipe allows. Just wanted to make sure there wasn't some issue that would prevent a scenario like transferring 5Gb/s through the sfp+ port and 2.5Gb/s through the 2.5GBe interface simultaneously since the total throughput is just 7.5Gb/s, assuming the CPU can handle it etc etc etc.Depends on how you have the ports configured.
If you have stuff "switching", like vlans etc then you should get full wirespeed.
Else if you need to process traffic then the bottleneck is that 10Gb full duplex link to the cpu plus any load on the cpu itself..